He won't have full adult rights. Independent adults have control over their finances, they decide where they live, they decide when they get up, they decide what they wear, they decide when they go to bed, they decide how they spend their time, and with whom. As an independent adult, if I want to go to the 24 hour supermarket at 2am because I'm out of chocolate, I can.
In residential care, you get little to none of this. You are woken up by whoever is on shift that morning at the time they think is appropriate. Depending on how good the setting is, you might get to ask for a lie in, because there is a huge gap between what is best practice (letting people have some autonomy over when to get up) and what happens on the ground when CQC inspectors aren't looking. You pick your clothes from what's offered (if the staff can be bothered to follow the care plan that says you get a choice of at least two outfits), you eat breakfast from what the setting provides. Then you sit in an armchair with nothing to do while the carer on shift doomscrolls on their phone. Then it's lunch time. Maybe you get away from your own four walls for a trip outside before dinner.
The trip to the zoo would have been pre-arranged on his behalf as a beneficial activity by the care setting. He may not even have had any input into the decision beyond a staff member saying "would you like to go to the zoo next month"? If you live somewhere like that, you can't say "I want to go to the zoo" and go that day. It will have been arranged around the staffing rota, staff annual leave and the health appointments of anyone else resident at the same setting.